Direct fired unit heater



July 23, 1946. A. A. OLSON DIRECT FIRED UNIT HEATER Filed Aug. 2, 1941 ARTHUR A. OLSON- Patented July 23, 1946 pmno'r FIRED UNIT HEATER Arthur A. Olson, Youngstown, Ohio Application August 2, 1941, Serial No. 405,203

. 1 This invention relates to air heating furnaces and more particularly to such furnaces of the direct fired unit heater type in which the air to a be heated is brought in close proximity with heat conducting and radiating Surfaces which are in turn directly exposed to the combustion, of the fuel employed, all the parts being grouped in a unitary and self-sufficient assembly. a

The present invention relates directly toldirect fired unit heaters of the general type disclosed in United-States Patent No. 2,146,122 to Leif Lee and involves a specific improvement in the air heating furnace construction shown therein.

In the air heating furnace shown in the said 7 patent, combustion of the fuel takes place in an arched-shaped combustion chamber and the exhaust passages forthe products of combustion are so arranged that the gases are caused to move downwardly along the sidewalls of the chamber beyond and below the combustion zone and inuniformly distributed relation throughout, the length of the side walls of the combustion chamber. Thus, the gaseous products of combustion are blanketed along either side wall and moved relative thereto in wiping contact. Following the contour of the arched-shaped combustion chamber and substantially uniformlyspaced therefrom is an outer casing which restricts the flow of the air to be heated in close proximity and/ or wiping contact with the outer surfaces of the wallsof the combustion chamber and for maximum efficiency, the flow of air about the side walls of the chamber is likewise substantially uniformly distributed throughout the length of the walls. This feature of operation is accomplished by properly disposing the air moving means employed and by properly designing and arranging the air inlets and outlets for the spaces between the inner and outer casings of the furnace, including the interconnection between the air moving means and the spaces. Although the air moving means is normally employed to force the air through the spaces by positive pressure, it is sometimes desirable to locate the moving means adjacent the exit passage of the spaces thereby creating a negative pressure in the spaces for the purpose of drawing the air therethroughh Also, for the accomplishment of the objects generally stated, it is more practical to employ air moving means of the turboblower or squirrel cage type, rotatable about an axis extending generally parallel withthe principal axis of the furnace chamber and in the case of furnaces of substantial capacity at least, it is desirable to employ two or more blowers spaced substantially uniform along thesaidaxes. Inthis 2 Claims. (01. 126-110) way uniform distribution of the air along the longitudinal extent of the above mentioned spaces 1 is facilitated.

The primary object of the invention is to increase the over-all efficiency of a direct fired air heating furnace of the general type outlined above and this object is accomplished in accordance with the invention by incorporating heat exchanging or economizer tubes in the unitary assembly, which tubes are positioned longitudinally of the furnace and serve to conduct the gaseous 1 products of combustion aS the latter issue from the combustion chamber casing through the lon-Z gitudi nally extending air stream created by the operation of the air moving means.

A further and more, specific object of the invention is the provision in a direct fired air heating furnace of the general type mentioned aboveof trated a preferred embodiment of theinvention,

In the drawing:

Figure is a View in side elevation of a representative embodiment of the invention, parts being broken away to better illustrate the internal construction of the furnace; and v l l I Figure 21 a transverse section through the furnace along theline IIII of Figure 1. I

Referring to the drawing which illustrates, a representative embodiment of the invention,,ref-- erence numeral [0 indicates a combustion chame ber casing which vis generally inverted lJ-shaped in section, as shown in Figure 2, and which is preferably provided with circumferentially ex-- tending corrugations to increase. the heat eX- changing surfaces, Secured, preferably by welding, to the outer surface of the casing I0 are a plurality of deflecting fins ll which are operative to deflect the air moving upwardly along the side walls of the casing into intimate wiping contact with the outer surfaces of the walls. Positioned within the lower portion of the casing ID is an elongated fire box l2 constructed of; re-

fractory brick and supported on the floor plate l3 of the casing I0, As indicated, in Figure 2,

the,- side walls ofl the fire box 12' are spacedzinheated.

j wardly from the side wall of thecasing ID to 1 provide thin elongated passages M for the downward passage of the products of combustion in.

l4 through An outer casing l8 having'its walls adjacen to but uniformly spaced from the walls of the casing I is provided to form restrictive passages l9 on either side of the furnace for theair to be H along either side of the furnace. air fiow, in conjunction with the opposing 1' blanket flow of the products ofcombustion along the inner surfaces of theisaid walls of the cas- 2 ing Ill, provides an efficient heat transfer and has resulted in substantial success in numerous commercial embodimentssome of which have 1 been constructed in very large capacities.

prior patent referred to above, and that if 'de- Casing I8 extends throughout the length of the inner casing I 0 and it should be apparent that the air to be heated moves in 1 through the furnace in thin blanket formation This type of By reason of the fact that in the particular type of furnace to which the invention is especially ap-. plicable, the air stream is of substantially uniform density throughout the longitudinal extent thereof the positioning of the heat exchanging or economizer tubes in the air stream and in a direction longitudinally of the furnace results in certain definite advantages relating. to economy and efiiciency whichshould be obvious. It should be understood that various changes may be made in the illustrated embodiment of the invention j withoutdeparting from the spirit or scope of the invention. For example, in addition'to the alternatives mentioned above, the tubes 26 may be sired, the direction of air flow through the heating unit may be reversed. In either construction,power means is employed to circulate the air through the passages either by pressures above or below atmospheric pressure and in the embodiment specifically illustrated, the air mov-' ing means-comprises a pair of spaced squirrel cage type of blowers .20 mounted on a common shaft extendinglongitudinally below the furnace proper. This shaft, indicated by reference numeral 2|, is driven by motor 22. Also driven by shaft 2| is any exhaust fan 23 which i operative to withdraw theproducts of combustion from the casing l0.

In accordance with the illustrated embodiment of the invention,'a duct extends downwardly along one end of the furnace and communicates with the Central duct which is positioned below the fire box l2. 'A portion of duct 24 consists of a, header 25 from which extends a plurality of heat exchanging tubes 26 which, as shown, ex-

tend longitudinally of the furnace across the air inlet to the passages IS. The opposite ends of the tubes 26 open into a collector 21 on the opposite end of the furnace and the inlet to the exhaust fan'23 is connected with the collector 2'! whereby the products of combustion are drawn through the tubes 26 before passing out of the upwardly and outwardlyto facilitate the accomplishment of this objective;

1 It'should now be apparent that I have provided 1 certain improvementsin direct fired unit heaters 1 which accomplishesthe objects initiallysetout.

positioned between the inner and outercasings in either a single group or in separated groups and further, it is contemplated that the tubes may be so designed or alternatively suitable deflecting surfaces may be secured to the tubes 50 that the defiecter fins, i. e. the fins H which are attached to the inner casin maybe dispensed'with while retaining the high efficiency of this type offurnace. Reference should therefore be had to'the appended claims in determining the scope of the invention.

What Iclaim is: r

1. An air heating furnace comprising a casing generally inverted U-shaped in section defining a combustion chamber, a fire box within the lower portion of said casing, and havingsidewalls ad jacent. to but uniformly spaced from' the side walls of said casing to provide a thin restrictive but wide passage for heating gases on either side of said furnace, duct means below said fire box and connected with said passages throughout the width, thereof thereby insuring uniform flow in said passages throughout the extent thereof, an outer casing for said furnace adjacent to but uniformly spaced from said first mentioned casing providing a wide passage for athin blanket of air on either of the. sides of said furnace, an air inlet extending throughout the width of each of said air passages at the bottom thereof, an air outlet extending throughout the Width of said last mentioned passages at the top thereof, means to circulate a uniform volume of air through said last mentioned passages, meansforming'an air chamber below said inlets, a, plurality of heat exchanging tubes positioned in said chamber and extending throughout the width of said passages whereby the air flowing into said inlets flows over said tubes substantially at right angles thereto,

said tubes connecting with said duct means to conduct the products of combustion away from said duct means, means to distribute the air flowing into said chamber substantially uniformly throughout the'length of said tubes, means to conduct air to be heated into said chamber, and

' a V-shaped air stream divider positioned in said chamber centrall below said first mentioned casing,- said divider extending longitudinally throughout the length of said casing and having its wings terminated substantially at the lower ends of the side walls of said first mentioned casing whereby air entering said sp-ace will be divided equally between saidinlets, said heat exchanging tubes being positioned symmetrically about and immediately below said divider.

2."An air heating furnace comprising 'a casing generally inverted U-shaped in section defining a combustion chamben'an outer casing adjacent to but uniformly spaced from said first mentioned casing providing a widepassage'fora thin blanket of air on either of the sides of said furnace, an air'inlet extending throughout the width of each of said air passages at the bottom thereof, an air outlet extending throughout the width of said last mentioned passagesat the top thereof, means to circulate a uniform volume of 'air through said air passages, means forming an air chamber below said inlets, a plurality of heat exchanging tubes positioned in said chamber and extending throughout the width of said inlets whereby the air flowing into said inlets flows over said tubes substantially at right angle thereto, said tubes connecting with said combustion chamber to withdraw the products of combustion therefrom, means to distribute the air flowing into said chamber substantially uniformly throughout the length of said tubes, and a V-shaped air stream divider positioned centrally below and extending longitudinally throughout the length of said first mentioned casing and having it wings terminated substantially at the lower ends of the side walls thereof whereby air entering said space will be divided between said inlets, said heat ex- 

